The discussion revolves around the observation of an absorption line of hydrogen in the spectrum of a galaxy, comparing its wavelength observed at 494.9 nm to a laboratory measurement of 490 nm. Participants explore implications regarding the motion of the galaxy based on these wavelength differences.
The conversation includes various interpretations of the wavelength changes and their implications for the galaxy's movement. Some participants provide guidance on precision in calculations, while others seek clarification on the implications of their findings.
Participants mention that the problem is part of a long-distance learning course in GCSE Astronomy. There are discussions about the precision of calculations and the significance of the speed of light in the context of the problem.
I am doing a GCSE Astronomy course, but it's not for school. It is a long distance learning course, and this is a question on one of the assignments.mfb said:What do you think?
Is this homework?
Thanks for moving it to the more specific section. The wavelength would get shorter. What do you mean about the digit?mfb said:I moved the thread to the homework section.
Does the wavelength get longer or shorter if the galaxy is moving towards us?
You might want to keep one more digit precision in the calculations.
But the wavelength you are given here gets longer.Atominate said:The wavelength would get shorter.
Your rounding is quite imprecise.Atominate said:What do you mean about the digit?
Right.Atominate said:I see, so the wavelength is increasing by 4.9nm meaning the Galaxy is moving away?
No, that is fine. The 0.01 relative shift you calculated is imprecise. There is a huge difference between 0.005 and 0.0149 (a factor of 3!) but both would get rounded to 0.01 if you just keep two digits after the decimal point.Atominate said:I've been told to consider the speed of light as 300,000km/s for this question. Is this what you mean about rounding?
I don't understand what you mean. I am not rounding any of the figures. Can you explain?mfb said:No, that is fine. The 0.01 relative shift you calculated is imprecise. There is a huge difference between 0.005 and 0.0149 (a factor of 3!) but both would get rounded to 0.01 if you just keep two digits after the decimal point.
Okay. Thanks for your help.mfb said:Ah I see, it happens to be "exactly" 0.01. I would still keep one more digit and write it as 0.010.